In several industries, the manufacturing processes for metal products finished by processes such as machining, transformation and cutting of intermediate products generate significant amounts of chips and machining off-cuts. In this text, this waste is indicated by the term “scrap” which is used in standard EN 12258-3 to indicate the products for aluminum recycling. The aircraft and space industries in particular generate a significant amount of scrap because many structural parts and components of an aircraft are obtained by integral machining of massive parts. However scrap is often difficult to recycle directly because it is mixed with other aluminum alloys or other materials used in aeronautics such as stainless steels and titanium (Wilson et al. Journal de Physique C-75 1987). Waste from machining aeronautical alloys, for example, is recycled in aluminum-silicon alloys designed for molded products, in particular for the automobile industry. This recycling method is the usual one for scrap recycling. It leads to a partial loss in value of the metal.
It is also possible to manufacture aluminum alloy products designed for aeronautical and space applications from scrap from the aircraft industry in an integrated recycling process. Successive recycling of series 2XXX or series 7XXX alloys in this integrated process generally leads, however, to an increase in the content of certain impurities such as iron and silicon. During machining, handling and storage phrases, it frequently happens that dust gets incorporated into the scrap and this dust is generally rich in iron and silicon which are two very common elements in any industrial environment. In the same way, during the process of scrap smelting, contact with tools and furnace walls frequently produces an increase in the iron and silicon content.
In addition, new grades of series 2XXX or series 7XXX alloys for which the iron and silicon content can be kept below 0.07% by weight, or even, in certain cases, below 0.05% by weight, prove difficult or even impossible to manufacture from scrap using current recycling processes.
The application of purification operations in a molten metal bath obtained by scrap smelting has been considered.
Patent applications JP07166259, JP07207378, JP09178149 and JP09263853 (Furukawa Electric) seek to solve the problem of recycling plated sheets designed for the manufacture of heat exchangers by brazing. The scrap from these products contains several percent of silicon by weight, which makes recycling difficult. Processes including a fractional, crystallization stage and a final stage involving pressing the crystals formed to eject the residual liquid are described in these patent applications. These processes aim to eliminate the silicon. The special problems posed by the purification of iron are not dealt with in these requests. Other segregation processes including a cooling stage using a molten salt have also been considered, in particular for the production of pure metal of type P0101, the only impurities in which are iron and silicon with a content lower than 0.1% by weight (see EP 1.520.052, EP 1.520.053 and WO 2005/049875, Corus Technology). The use of a molten salt significantly complicates this type of recycling operation.
Request PCT WO 2005/095658 (Corus Technology) describes the principle of a process in which the molten metal to be purified is cooled in order to simultaneously form purified crystals and crystals containing a foreign element (such as an element forming intermetallic compounds) and in which these two types of crystals are separated by a solid-solid separation technique. The solid-solid separation technology is not described in this patent application.
The use of an additive to force the formation of precipitates and thereby facilitate their separation has also been considered. Adding Mn is encouraged in U.S. Pat. No. 5,741,348 (Hoogovens) and EP 1 288 319 (Corus Technology) and in patent application JP0835021 (Agency of Ind science & technol) to form intermetallic precipitates containing iron in order to eliminate it. These processes are not applicable in complex systems such as aeronautical alloys because of the number of intermetallics to be taken into consideration.
Furthermore, adding boron to eliminate particular elements such as peritectic elements has been considered. Patent EP 1 101 830 (Pechiney Rhenalu) describes a manufacturing process for an intermediate product in a given alloy of series 7XXX from recycling products. In order to be able to recycle off-cuts from different alloys of the 7XXX series without having to carry out sorting, this patent describes a process including at least one refining stage of said recycling products making it possible to reduce the content of a peritectic element such as Cr or Zr with the help, for example, of a selective precipitating agent including boron.
The recycling of scrap from the aircraft industry poses several special problems which have not been solved in the prior art, in particular:                industrially decreasing the content of elements which would not allow recycling in equivalent grades such as Fe and Si, in particular to obtain Fe and Si contents lower than 0.1% by weight and preferably lower than 0.05% by weight,        not decreasing the content of elements common to the majority of these alloys (Zn, Mg, Cu in series 7XXX; Cu and Mg in series 2XXX),        in certain cases, not decreasing the content of certain expensive elements (Li, Ag, Sc) that may be used in certain alloys.        
It would therefore be useful to invent a recycling process including a stage for iron and silicon purifying of aluminum alloy scrap of series 2XXX or series 7XXX, without eliminating the additive elements such as zinc, copper and magnesium, for example.
The applicant therefore sought a manufacturing process for intermediate products using scrap from the aircraft industry which would facilitate recycling of series 7XXX and series 2XXX alloys.